A species of potassium channel that is dependent on adenosine triphosphate (ATP) was first described in cardiac muscle by Noma A. (1983), "ATP-regulated K.sup.+ channels in cardiac muscle," Nature 305: 147-148. This channel has attracted increasing interest due to its unusual and close association with cell metabolism. Ashcroft, F. M. (1988), "Adenosine 5-triphosphate-sensitive potassium channels," Ann. Rev. Neurosci. 11: 97-118. It is now well established that ATP-sensitive potassium channels are present in diverse tissues i.e. cardiac muscle, (Kakei M. and Noma A. (1984) "Adenosine 5'-triphosphate-sensitive single potassium channel in the atrioventricular node cell of the rabbit heart," J. Physiol. 352: 265-284, Noma A. and Shibasake, T. (1985), "Membrane current through adenosine-triphosphate-regulated potassium channels in guinea-pig ventricular cells," J. Physiol. 363: 463-480), pancreatic beta cells (Findlay, I., Dunne, M. J., and Petersen, O. H. (1985a), "ATP-sensitive inward rectifier and voltage- and calcium activated K.sup.+ channels in cultured pancreatic islet cells," J. Memb. Biol. 88: 165-172; Dunne, M. J., Findlay, I., Petersen, O. H. and Wollheim, C. B. (1986), "ATP-sensitive K.sup.+ channels in an insulin-secreting cell line are inhibited by D-glyceraldehyde and activated by membrane permeabilization." J. Memb. Biol. 93: 271-279; Ashcroft, F. M. et al (1984), "Glucose induces closure of single potassium channels in isolated rat pancreatic .beta.-cells," Nature 312: 446-448); skeletal muscle (Sturgess, N. C., Ashford, M. L. J., Cook, D. L. and Hales, C. N. (1985), "The sulphonylurea receptor may be an ATP-sensitive potassium channel," Lancet 8435: 474-475) and smooth muscle (Standen, N. B., Quayle, J. M., Davies, N. W., Brayden, J. E., Huang, Y. and Nelson, M. T. (1989), "Hyperpolarizing vasodilators activate ATP-sensitive K.sup.+ channels in arterial smooth muscle," Science 245: 177-180). More recently, indirect evidence has suggested that the ATP-sensitive channel may also be present in the brain: sulfonylureas, which are potent blocking agents of this channel in heart and beta cells, display selective binding in certain brain regions (Mourre, C., Ben Ari, Y., Bernardi, H., Fosset, M. and Lazdunski, M. (1989), "Antidiabetic sulfonylureas: localization of binding sites in the brain and effects on the hyperpolarization induced by anoxia in hippocampal slices," Brain Res. 486: 159-164) and indeed an endogenous ligand for a central sulfonylurea receptor has been described (Virsolvy-Vergine, A., Bruck, M., Dufour, M., Cauvin, A., Lupo, B. and Bataille, D. (1988), "An endogenous ligand for the central sulfonylurea receptor," FEBS Letters 242: 65-69). It has also been found that sulfonylurea binding sites appear to be highest in regions of the brain associated with the control of movement, i.e. motor cortex, cerebellar cortex, globus pallidus and substantia nigra (Mourre et al., supra, 1989).
Despite intensive research into the causes and cures for Parkinson's disease, the actual homeostatic mechanisms of physiological and indeed pathological neuronal regulation within the substantia nigra remain obscure. In the brain, the substantia nigra has the highest density of binding sites for the sulphonylurea, glibenclamide (Mourre, C. et al, Brain Res. 486, 159-164 (1989)), a selective blocker of K.sub.ATP (Sturgess, N., et al, Lancet ii 8453, 474-475 (1985); Schmid-Antomarchi, H., et al Biochem. Biophys. Res. Commun. 146, 21-25 (1987); and Weille de, J., et al, Proc. Natl. Acad. Sci. USA 85, 1312-1316 (1988)). It is thus possible that in the substantia nigra this channel, which has an unusual and close association with cell metabolism (Ashcroft, F. M., Ann. Rev. Neurosci. 11, 97-118 (1988)), may play a pivotal role in neuronal regulation.